Convergence is the process of all routers coming to agreement on optimal routes in a network. When a network event causes
routes to become available or unavailable, routers send routing update messages through the network that cause routing algorithms
to recalculate optimal routes. Eventually all the routers agree on the routes as well as the network topology. Fast convergence
benefits network performance. Routing algorithms that converge slowly may cause temporary routing loops or temporary network
The process of network convergence can be divided into three separate stages:
Routing change detection: The speed at which a device on the network can detect and react to the failure or modification
of one of its own components, or to a topology change caused by the failure or modification of a component on a routing protocol
Routing change notification: The speed at which the failure or topology change in the previous stage can be communicated
to other devices in the network.
Alternate path calculation: The speed at which all devices on the network, having been notified of the failure or topology
change, can process the information and calculate an alternate path through which data can flow.
An improvement in any one of these stages provides an improvement in overall convergence. In addition to a basic configuration
task that is recommended as a first step in configuring an IS-IS router with best practice parameters for achieving fast convergence,
several recommended configuration tasks are grouped according to the stage of network convergence they can improve. For more
information, see the following modules:
"Setting Best Practice Parameters for IS-IS Fast Convergence"
"Reducing Failure Detection Times in IS-IS Networks"
"Reducing Link Failure and Topology Change Notification Times in IS-IS Networks"
"Reducing Alternate-Path Calculation Times in IS-IS Networks"